Biochemistry for Dental Students

1. Dental Biochemistry 2 – (Lec. 8)
Minerals
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2. • A few minerals are required for the normal growth and
maintenance of the body. If the daily requirement is more than
100 mg, they are called major elements.
• If the requirement of certain minerals is less than 100 mg/day,
they are known as minor elements or micro-minerals or trace
elements.
• Major elements Trace elements
1. Calcium 1. Iron
2. Magnesium 2. Iodine
3. Phosphorus 3. Copper
4. Sodium 4. Manganese
5. Potassium 5. Zinc
6. Chloride 6. Molybdenum
7. Sulfur. 7. Selenium
8. Fluoride
• The following minerals are toxic and should be avoided:
aluminium, lead, cadmium and mercury 2

3. CALCIUM (Ca++)
• Total caIcium in the human body is about 1 to 1.5
kg, 99% of which is seen in bone and 1% is
extracellular.
• Sources of Calcium
• Milk is a good source for calcium. Egg, fish and
vegetables are medium source for calcium. Cereals
(wheat, rice) contain only small amount of calcium.
• Daily Requirement of Calcium
• An adult needs 500 mg per day and a child about
• 1200 mg/day. Requirement may be increased to
1500 mg/day during pregnancy and lactation. 3

4. Absorption of Calcium
• Absorption is taking place from the first and
second part of duodenum. Absorption requires a
carrier protein, helped by calcium-dependent
ATPase.
• Factors affecting absorption of calcium are:
i. Vitamin D: Calcitriol induces the synthesis of
the carrier protein (Calbindin) in the intestinal
epithelial cells, and so facilitates the absorption
of calcium.
ii. Parathyroid hormone: It increases calcium
transport from the intestinal cells.
iii. Acidity: It favors calcium absorption.
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5. iv. Phytic acid: It is present in cereals. It reduces
uptake of calcium. Cooking reduces phytate
content.
v. Oxalates: They are present in leafy vegetables,
which cause formation of insoluble calcium
oxalates; so absorption is reduced.
vi. Phosphate: High phosphate content will cause
precipitation as calcium phosphate.
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6. Functions of Calcium
1. Activation of enzymes:
• various regulatory kinases.
• pancreatic lipase.
• enzymes of coagulation pathway.
• Rennin (milk clotting enzyme in stomach).
2. Muscles:
• Calcium mediates excitation and contraction of
muscle fibers.
• Calcium decreases neuromuscular irritability.
• Calcium deficiency causes tetany. 6

7. 3. Calcium is necessary for transmission of nerve
impulses through synaptic region.
4. Secretion of hormones: Calcium mediates
secretion of insulin, parathyroid hormone, etc. from
the cells.
5. Second messenger: Calcium and cyclic AMP are
second messengers of different hormones. One
example is glucagon.
6. Coagulation: Calcium is known as factor IV in
blood coagulation cascade.
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8. 7. Myocardium: Ca+ + prolongs systole. In
hypercalcemia, cardiac arrest is seen in systole. This
fact should be kept in mind when calcium is
administered intravenously. It should be given very
slowly.
8. Bone and teeth: The bulk quantity of calcium is
used for bone and teeth formation. Bones also act
as reservoir for calcium in the body.
(N.B. Osteoblasts induce bone deposition and
osteoclasts produce demineralization).
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9. Factors Regulating Blood Calcium Level
(A) Vitamin D
• The active form of vitamin D is called calcitriol.
• The calcitriol induces a carrier protein in the
intestinal mucosa, which increases the absorption
of calcium. Hence blood calcium level tends to be
elevated.
(B) Parathyroid Hormone (PTH)
• i. This hormone is secreted by the four parathyroid
glands.
• ii. Control of release of the hormone is by negative
feedback by the ionized calcium in serum.
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10. Mechanism of action of PTH
i. PTH acts through cyclic AMP. Increase Ca absorption
from intestine.
ii. PTH and bones:
• In the bone, PTH causes demineralization or
decalcification.
• It induces pyrophosphatase in the osteoclasts. The
number of osteoclasts are also increased.
• Osteoclasts release lactate into surrounding medium
which solubilizes calcium.
• PTH also causes secretion of collagenase from
osteoclasts. This causes loss of matrix and bone
resorption. 10

11. iii. PTH and kidney:
• In kidney, PTH causes decreased renal excretion
of calcium and increased excretion of phosphates.
• The action is mainly through increase in
reabsorption of calcium from kidney tubules.
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12. (C) Calcitonin
• i. It is secreted by the thyroid parafollicular or clear cells.
Calcitonin is a single chain polypeptide. It contains about
32 amino acids.
• ii. Calcitonin secretion is stimulated by serum calcium.
• iii. Calcitonin level is increased in medullary carcinoma of
thyroid and therefore is a tumor marker.
• iv. Calcitonin decreases serum calcium level. It inhibits
resorption of bone. It decreases the activity of
osteoclasts and increases that of osteoblasts.
• v. Calcitonin and PTH are directly antagonistic. The PTH
and calcitonin together promote the bone growth and
remodeling.
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13. Calcitonin, Calcitriol and PTH Act Together
• When blood calcium tends to lower, PTH secretion
is stimulated and calcitonin is inhibited; bone
demineralization leads to entry of more calcium
into blood.
• When blood calcium is increased, PTH is inhibited
and calcitonin is secreted, causing more entry of
calcium into bone.
• Bone acts as the major reservoir of calcium
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14. (D) Phosphorus There is a reciprocal relationship
of calcium with phosphorus. The ionic product of
calcium and phosphorus in serum is kept as a
constant. (In normal adults, calcium = 10 mg/dl x
phosphorus 4 mg/dl; so ionic product is 40).
(E) Children
In children, the calcium level tends to be near the
upper limit. In children, ionic product of calcium
and phosphorus in blood is about 50 (instead of 40
in normal adults).
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15. Homeostasis of serum calcium
Gut
↓ ← D ← PTH
PTH
Bone ↔ Serum calcium ← Reabsorption of
D. C. Calcium from
kidney tubules
C= Calcitonin; D= Vitamin D; PTH= Parathyroid
hormone
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16. IRON (Fe)
Distribution of Iron
• Total body iron content is 3 to 5 gm, 75% of which
is in blood. Iron is present in almost all cells.
• Heme containing proteins are hemoglobin,
myoglobin, cytochromes, cytochrome oxidase,
catalase.
• Non-heme iron containing proteins are
transferrin, ferritin, hemosiderin.
• Blood contains 14.5 g of Hb per 100 ml. About
75% of total iron is in hemoglobin, and 5% is in
myoglobin and 15% in ferritin.
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17. Factors Influencing Absorption of Iron
• i. Reduced form of iron: Only Fe++ (ferrous) form
(reduced form) is absorbed. Fe+++ (ferric) form is not
absorbed.
• ii. Ascorbic acid: Ferric ions are reduced with the
help of gastric HCl, and ascorbic acid. Therefore
these will favor iron absorption.
• iii. Interfering substances: Iron absorption is
decreased by phytic acid (in cereals) and oxalic acid
(in leafy vegetables) by forming insoluble iron salts.
Calcium, copper, lead and phosphates will inhibit
iron absorption.
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18. Mucosal Block Theory
• i. Duodenum and jejunum are the sites of
absorption. Iron metabolism is unique because
homeostasis is maintained by regulation at the
level of absorption and not by excretion. No other
nutrient is regulated in this manner.
• ii. When iron stores in the body are depleted,
absorption is enhanced. When adequate quantity
of iron is stored, absorption is decreased. This is
referred to as "mucosal block" of regulation of
absorption of iron.
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19. • iii. Iron in the intestinal lumen enters the
mucosal cell in the ferrous state. This is
bound to transferrin molecule present on
the brush border surface of intestinal cell.
• iv. This is then complexed with a specific
receptor. The iron-transferrin-receptor is
internalized. Iron is taken in by the cells, and
receptor molecules are externalized.
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20. • v. This receptor mediated uptake is more in
iron deficient state. When iron is in excess,
receptors are not produced; this is the basis
of "mucosal block".
• vi. The absorbed iron binds with apoferritin,
to form ferritin. It is kept temporarily in the
mucosal cell. If there is anemia, the iron is
further absorbed into the blood stream.
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21. Iron Transport in Blood
• i. Transport form of iron is transferrin. It is a beta1
globulin. Normal plasma level of transferrin is 250
mg/100 ml. In iron deficiency, this level is increased.
• ii. In iron deficiency anemia, Total iron binding
capacity (TIBC) is increased (transferrin level is
increased); but serum iron level is reduced.
• iii. Transferrin takes up iron with the help of
ferroxidase.
• In blood, ceruloplasmin is the ferroxidase, which
oxidizes ferrous to ferric state.
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22. Ferroxidase
• Apo-transferrin ----------------------------------------------------------------------------------------1) Transferrin combined
• +2 Fe+++ 1/2 02 with 2 Fe+++ + H2O
• Storage of Iron
• The storage form is ferritin. It is seen in
intestinal mucosal cells, liver, spleen and
bone marrow.
• In iron deficiency anemia, ferritin content is
reduced.
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23. Iron Is Conserved
• i. When RBC is lysed, hemoglobin enters into
circulation. Being a small molecular weight
substance, Hb will be lost through urine. To
prevent this loss, Hb is immediately taken up by
haptoglobin (Hp).
• ii. When the globin part is removed from Hb, the
heme is produced, and is released into circulation.
In order to prevent its excretion through urine,
heme is bound with hemopexin.
• iii. Iron is very precious for biological systems.
Hence these elaborate mechanisms are necessary
for conservation inside the body.
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24. Excretion of Iron
• i. Iron is a one-way element. That is, very little of it is
excreted.
• The regulation of homeostasis is done at the
absorption level.
• Almost no iron is excreted through urine. Feces
contains unabsorbed iron as well as iron trapped in
the intestinal cells.
• ii. Any type of bleeding will cause loss of iron from the
body. Menstrual flow is the major cause for loss of
iron in women.
• iii. All the cells in skin contain iron. The upper layers of
skin cells are constantly being lost, and this is another
route for iron loss from the body.
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